Offshore platform structure



June 25, 1963 1. c. POGONOWSKI 3,094,847

\ OFFSHORE PLATFORM STRUCTURE Fi led Oct. 19, 1960 2 Sheets-Sheet 1 hzlINVENTOR l. C. POGONOWSKI BY Q-J-(I'M HIS AGENT June 25, 1963 1. c.POGONOWSKI 3,

OFFSHORE PLATFORM STRUCTURE Filed 001,. 19, 1960 2 Sheets-Sheet 2 FIG. 4

A i I FIG. 5 FIG. 6 FIG. 7

FIG. IO

INVENTOR l. C. POGONOWSKI HIS AGENT 3,094,847 OFFSHGRE PLATFORMSTRUCTURE Ivo C. Pogonowski, New Orleans, La., assignor to Shell OilCompany, New York, N.Y., a corporation of Delaware Filed Oct. 19, 1960,Ser. No. 63,616 4 Claims. (Cl. 61-46) This invention relates to marinefoundation structures and pertains more particularly to oifshoreplatforms for drillingoil and gas wells and to methods for constructingplatforms of this type.

At present, one type of a stationary platform structure commonly usedfor offshore drilling or producing of wells makes use of a substructurewhich is constructed in the form of a large template, preferablycomposed of a single section comprising .a group of spaced hollow steelcolumns rigidly held together by structural cross-bracing. Piles arethen driven through the hollow template legs or columns to the depthrequired for foundation support purposes The piles are then fixedlysecured to the template, preferably by welding and then cut off atpredetermined levels. The columns of the template are normally made of apredetermined length of pipe or casing so as to extend from the oceanfloor at the offshore drilling location to a point above the averagewave level.

Mounted upon the substructure formed by the template and piles is alarge platform on which drilling or producing operations are con-ducted.The platform is generally constructed of a plurality of parallelstructural trusses extending longitudinally and transversely of the areaof the platform and intersecting each other at a plurality of points toform a generally rectangular box-like open-work structure having asurface area of required dimensions for its intended use as a workingplatform. This structural framework of the platform is then covered bysuitable flooring material upon which a conventional drilling derrickand suitable drilling or producing equipment may be mounted. It iscommon for the platform to have a plurality of legs extending downwardlytherefrom which are so constructed that they are in alignment with andseat within the tops of a plurality of legs or columns of the templateor in the piles installed therein.

Offshore platform structures of the above-described type utilizing aunitary template through which piles are driven and on which a platformis mounted have been used for several years in drilling and producinglocations on the Continental Shelf along the coasts of Louisiana andTexas. The well locations are generally several miles from shore. Thesetemplates are of enormous weight and as the selected drilling locationshave been in deeper and deeper water it has been found to be impossibleat some water depths to transport and install an offshore platformstructure of the template type because of the great size and weight ofthe template. Merely to divide the template into a number of sectionsthat were installed separately and connected above sea level at thedrilling location did not prove efiicient as it was difiicult and almostimpossible to align exactly the various segments of the structure. Decksections consequently did not have the proper stress carrying capacitybecause of misalignment of the load carrying trusses. Also there is nounder water continuity of a sectionalized structure of this type thusreducing its ability to withstand forces 3,094,847 Patented June 25,1963 due to wind and wave action and reducing the load carryingcapacity.

It is therefore a primary object of the present invention to provide anoffshore platform structure consisting of a plurality of structuralsegments adapted to be aligned exactly with each other both above andbelow the surface of the water.

A further object of the present invention is to provide a structure foran offshore platform on which a platform or deck section can be readilyand accurately aligned.

Another object of the present invention is to provide a method andapparatus for constructing an offshore platform structure possessingrigid continuity of structure below the water line to give it additionalstrength.

Still another object of the present invention is to provide an offshoreplatform structure composed of a plurality of sections whose weight andsize are that which could be handled by presently available constructionequipment at ofishore locations.

Another object of the present invention is to provide a sectionalizedoifshore platform structure wherein each section is provided with meansfor aligning and guiding it into place with the adjacent sections.

These and other objects of this invention will be understood from thefollowing description taken with reference to the drawing, wherein:

FIGURE 1 is an isometric view of one of the sub structure sections ofthe present oifshore platform structure positioned on the ocean doorwith the ends of all of the legs extending into the ocean floorsomewhat, while the tops of the long legs extend to a point above thesurfaceof the water;

FIGURE 2 is an isometric view of a mating section of the substructure ofthe present platform prior to it being raised and moved into position sothat its short upper legs can be lowered down over the guide piles drivethrough the short lower legs of the substructure section of FIG- FIGURE3 is a view in enlarged detail of a line or conduit positioned along oneof the legs of the substructure section of FIGURE 1. The line is to beused to cement underwater the annulus between the leg and the guidepile;

FIGURE 4 is a diagrammatic view illustrating a tug towing a barge with asubstructure section of the present invention to a position where thecrane barge may engage FIGURE 5 is a schematic view showing asubstructure section in place on the ocean floor while a crane bargelowers a second substructure section into place using guide piles as ahoming device;

FIGURE 6 is a schematic View illustrating the substructure of thepresent platform structure in place on the ocean floor at the time thedeck section is being lowered into place;

FIGURE 7 is a schematic View illustrating the completely assembledoffshore platform structure of the present invention;

FIGURE 8 is -a view taken in enlarged cross-sectional detail ofauxiliary guide means which may be employed to connect close to seabottom, two sections of the substructure of the present platform inaddition to guide piles which are cemented underwater to one section andwelded above water to the other;

FIGURE 9 is a schematic plan view of the completed 7 structure of FIGURE6 after the center pile has been installed through field installedbracing placed above water surface; and,

FIGURE is an exploded diagrammatic view of block-like elements whichwould fit together to form one type of an offshore platform inaccordance with the present invention as illustrated in plan view inFIGURE 9; the two upper blocks of FIGURE 10 representing thesubstructure sections shown in isometric view in FIG- URES 1 and 2.

Referring to FIGURE 1 of the drawing, a substructure section inaccordance with the present invention is shown as comprising a pluralityof long vertical tubular legs 11, 12, 13 and 14 in spaced relationshipwith each other and interconnected by cross-bracing members 15 arrangedin any suitable configuration, preferably in a manner to provide thegreatest rigidity to the structure. Positioned in spaced relationshipwith the long legs 11, 12, 13 and 14 and in planes parallel thereto andat right angles to each other are a plurality of short, lower, tubularvertical legs 16, 17, 18 and 19 which are connected together and to thelong legs by suitable bracing members 20. Additionally, diagonal braces21 are provided between the long legs or columns 11, :12, 13 and 14 andthe short legs or columns 16, 17, 18 and 13, if desired. Preferably, thelower ends of the diagonal braces 21 are in open communication with theinterior of the short legs 16, 17, 18 and 19 through the walls thereofso as to serve as conduit means for conducting a cement slurry to theshort lower legs 16, 17, 18 and 19. As shown in FIG- URE 3, asmall-diameter vertical conduit or cement pipe 22 may run down theoutside of the vertical column .11, the lower end of the cement pipebeing in open communication with the upper end of the diagonal brace 21through the wall thereof so that cement slurry may be injected into thediagonal brace 21 or through a smaller separate conduit and hence pumpeddown into the annulus of the short leg 16 and guide pile 35. Similarcement pipes would be provided for injecting cement slurry into theother short legs 17, 18 and 19.

In the event that the present offshore structure is to be positioned ona soft ocean bottom, it is preferred that vertical stabilizing steelplates or other suitable material be secured to the outside of the legsas at 23 and 24. These plate skirts 23 and 24 are illustrated in FIGURE1 as being positioned entirely below the bottom 25 of the body of waterwhile the long legs 11, 12, 13 and 14 extend upward-1y a distance atleast above the surface of the water 26. The section of FIGURE 1 isillustrated with piles 30, 31, 32 and 33 which extend through the longlegs 11, 12, 13 and 14 and deep into the ocean floor. Extendingoutwardly from the long legs 11, 12, 13 and 14 are bracing members 34which are adapted to be secured in any suitable manner, as by welding orbolting, to guide piles 35, 36, 37 and 38, after the guide piles havebeen driven into place through the lower short legs 16, 17, 18 and 19 ofthe substructure section. For ease of illustration, the guide piles 35,36, 37 and 38 have been shown in broken lines rather than solid lines.If desired, guide keyways 40 may be secured, as by welding, outwardly onthe lower short legs 16, 17, 18 and 19 and extend substantially thelength thereof. As shown in greater detail in FIGURE 8, the longitudinalkeyway 40 is designed to receive a key 41 carriedon a downward extensionfrom an upper short leg of an adjacent section. The lower short legs 16,:17, 18 and 19, while being illustrated as being about half the lengthof the long legs 11, 12, 13 and 14, may be of any length desired butpreferably extend at least above the ocean floor 25. The lower shortlegs .16, 17, 18 and 19 preferably include rubber packers properlyarranged to exclude soil from leg and guide pile annulus for effectivecemented connection.

'In FIGURE 2, a substructure section in accordance with the presentinvention is shown which would be installed adjacent the section shownin FIGURE 1. The substructure section of FIGURE 2 is provided with apair of short upper legs 42 and 43 which are short tubular members of alength and diameter to slide down over the guide piles 37 and 38 ofFIGURE 1 and form with the short lower legs 18 and 19 of FIGURE 1, acomplete leg having a length equal to the long legs 11, 12, 13 and 14 ofFIGURE 1, and the similar vertical tubular legs 44, '45, 46 and 47 ofFIGURE 2. The legs are interconnected with suitable braces 48 and thelower ends of the legs are provided with stabilizing skirts 49 and 50.In addition, the sbustructure section of FIGURE 2 is provided with twoshort lower legs 52 and 53 extending outwardly from the long legs of thesection at right angles to the direction taken by the upper short legs42 and 43. The lower short legs 52 and 53 are provided with keyways 40as described above, while the upper short legs 42 and 43 have downwardlyextending vertical support members 54 and 55 to which are attached keys41 as shown in FIGURE 8.

For ease of illustration, block-like segments A, B, C and D of FIGURE 10are shown in exploded view. Two of the parts A and B represent thesections shown in detail in FIGURES 1 and 2, respectively. It will beapparent from studying FIGURE 10 that section C is identical withsection B when turned at in a clockwise direction. Likewise, section Dis identical to section A if section A were turned upside down androtated 90. When two pairs of substructure sections as shown in FIGURES1 and 2 are put together in a manner illustrated in exploded view ofFIGURE 10', the resultant substructure of the offshore platform has aplan view as shown in FIGURE 9 of the drawing, with the central pile 56being added later. While the offshore platform structure of the presentinvention has been described with regard to having components which arerectangular in shape which are adapted to be assembled together to makea rectangular substructure and platform as shown in FIGURE 9, it is tobe understood that triangular or other configurations of the individualsubstructure sections may be employed, the essential feature being thatadjacent legs of any two sections be shorter than the other legs and beadapted to pass over or contain within their entire length a guide pileadapted to be secured to the short legs by welding above water orcementing underwater or in any other suitable manner to form a leg equalin length to the other vertical support members of the substructure.

In erecting an offshore platform structure of the present invention, thesubstructure sections and deck section are prefabricated on shore. InFIGURE 4 of the drawing, a tug 60 is shown as towing a barge 61containing the first section A (FIGURE 10) to the desired location wherea crane barge 62 is located. The crane picks up the section A and lowersit to the ocean floor as shown in FIGURE 1 of the drawing. Files arethen driven through legs 11, 12, '13 and 14 through the full lengththereof and deep into the ocean floor. The legs or columns 11, 12, 13and 14 may be sections of 33-inch diameter pipe while the piles driventherethrough are of pipe of a slightly smaller diameter (usually 30-inchdiiameter piles). The piles 3t}, 31, 32 and 33 are then welded to thetops of the long legs 11, 12, 13 and 14 and if necessary cut off so thatthey are all even. Piles 35, 36, 37 and 38 (FIGURE 1) are then driventhrough the short lower legs .16, 17, 18 and 19, which legs may be36-inch diameter pipe. By using the same size piles in the slightlylarger diameter short lower leg, it is possible to subsequently pumpcement into the short lower legs as will be described hereinbelow. Afterbeing driven, the piles 35, 36, 37 and 38 extend above the surface ofthe water.

As shown in FIGURE 5, the crane barge 62 then picks up section B ofFIGURE 10 or the section shown in FIGURE 2 and stabs the short uppersleeves 42 and 43 (FIGURE 2) over the top of the guide piles 37 and 38(FIGURE 1) at which time the keys 41 (FIGURE 8) carried on supportmembers 54- and 55 (FIGURE 2) will pass downwardly into keyways 40 onthe lower legs 18 and 19 (FIGURE 1) when the substructure B (FIGURE 5)is lowered by the crane barge 62 down through the water to .a level withthat of section A. With the two sections A and B (FIGURE 5) assembledtogether, piles would then be driven down through legs 44, 45, 46 and 47(FIGURE 9). Guide piles would thereafter be driven through the shortlower underwater legs 52 and 53 (FIG- URE 2) and section C (FIGURE 10)would be stabbed over these guide piles and lowered into place.Subsequently, piles would be driven through the long legs of sectionCand guide piles through the short legs. It is apparent that the lastsection D would be stabbed down over the guide piles extending upwardlyfrom sections A and C (FIGURE 10). After driving piles through all thelong legs of section D, all of the piles extending above the water linewould be welded or otherwise suitably connected to the legs throughwhich they extended. This applies to the guide piles as well as thepiles extending through the long legs of the various sections. At thesame time all lateral braces such as the braces 34 of FIGURE 1 would bewelded to short upper legs containing the guide piles.

Although not necessary in some installations, it is preferred that acentral pile 56 (FIGURE 9) be driven into the ocean floor and connectedby suitable lateral bracing to the adjacent legs. If desired a guidecollar may be installed in the center of the open square before drivingpile 56. After the erection of the substructure has been completed thedeck 70 provided with downwardly extending leg 71 is lifted by the cranebarge and lowered into place with the legs '71 aligning with and seatingto a short distance within some of the piles of the substructure. Due tothe size of many of these offshore installations it is necessary thatthe deck section be constructed in several mating sections which arelater connected in the field. With the deck section in place, suitableequipment is moved on the deck to connect hoses to the cement pipes 22(FIGURE 3) running down the legs of the substructure section and intothe cross-bracing members 21 which terminate in the underwater shortlegs of the substructure. Cement is then pumped down into the annulusbetween the piles and the underwater short legs of the substructure toobtain underwater continuity of the structure.

I claim as my invention:

1. An offshore platform structure comprising a framework-typesubstructure made up of a plurality of prefabricated tubular-leggedsubstructure sections adapted to be positioned on the floor of a body ofwater one at a time, each of said substructure sections having aplurality of long vertical legs of a length greater than the water depthwhen normally extending to the water bottom and a plurality of shortvertical legs, cross-bracing members securing the long and short legstogether to form a framework, at least one of said substructure sectionshaving at least two short legs arranged in the lower portion of thesection on one side thereof, a guide pile extending through each shortleg and into the floor, said short leg guide piles extending upwardly atleast above the water level, a pile extending through each of at leastsome of said long legs and into the floor, .and at least another of saidframework substructure sections having at least two Short legs arrangedon the upper portion of said section, said upper short legs being of aspacing and diameter sufficient to pass downwardly over the guide pilesin the lower short legs of said other substructure section, the combinedlength of said upper and lower short legs being no greater than thelength of said long legs.

2. An offshore platform structure comprising a framework-typesubstructure made up of a plurality of prefabricated tubular-leggedsubstructure sections adapted to be positioned on the floor of a body ofwater one at a time, each of said substructure sections having aplurality of long vertical legs of a length greater than the water depthwhen normally extending to the water bottom, and

a plurality of short vertical legs, cross-bracing members securing thelong and short legs together to form a framework, at least one of saidsubstructure sections having at least two short legs arranged in thelower portion of the section on one side thereof so that the bottoms ofthe short legs extend to the floor of the body of water, a guide pileextend-ing through each short leg and into the floor, said short legguide piles being secured to the short legs and extending upwardly atleast above the water level, a pile extending through each of aplurality of said long legs and into the floor, and at least another ofsaid framework substructure sections having at least two short legsarranged on the upper portion of said section, said upper short legsbeing of a Spacing and diameter suflicient to pass downwardly over theguide piles in the lower short legs of said other substructure section,said upper and lower short legs being arranged in coaxially displacedrelationship on said guide piles and being fixedly secured thereto toform a leg equal in length to the long legs of said substructuresections, .a horizontally-disposed deck section supported on saidsubstructure.

3. An offshore platform structure comprising a framework-typesubstructure made up of a plurality of prefabricated tubula-r-leggedsubstructure sections adapted to be positioned on the floor of a body ofwater one at a time, each of said substructure sections having aplurality of long vertical legs of a length greater than the water depthand a plurality of short vertical legs of a length less than the waterdepth, cross-bracing members securing the long and short legs to form aframework, at least one of said substructure sections having at leasttwo short legs arranged in the lower portion of the section on one sidethereof so that the bottoms of the short legs extend to the floor of thebody of water, a guide pile extending through each short leg and intothe floor, said short leg guide piles being secured to the short legsand extending upwardly at least to the height of the long legs, a pileextending through each of a plurality of said long legs and into thefloor, at least another of said framework substructure sections havingat least two short legs arranged on the upper portion of said section,said upper short legs being of a spacing and diameter suflicient to passdownwardly over the guide piles in the lower short legs of said othersubstructure section, said upper and lower short legs being arranged incoaxially displaced relationship on said guide piles and being fixedlysecured thereto to form a leg equal in length to the long legs of saidsubstructure sections, and a horizontally-disposed deck section mountedon and secured to the tops of a plurality of the legs of said joinedsubstructure sections.

4. An offshore platform structure comprising a framework-typesubstructure made up of a plurality of prefabricated tubular-leggedsubstructure sections adapted to be positioned on the floor of a body ofwater one at a time, each of said substructure sections having aplurality of long vertical legs of a length greater than the water depthand a plurality of short vertical legs of a length less than the waterdepth, cross-bracing members securing the long and short legs to form aframework, outlining a geometrical figure having a closed perimeter, atleast one of said substructure sections having at least two short legsarranged in the lower portion of the section on one side thereof so thatthe bottoms of the short legs extend to the floor of the body of water,a guide pile extending through each short leg and into the floor, saidshort leg guide piles being cemented in the short legs and extendingupwardly at least to the height of the long legs, a pile extendingthrough each of a plurality of said long legs and into the floor, atleast another of said framework substructure sections having at leasttwo short legs arranged on the upper portion of said section, said uppershort legs being of a spacing and diameter sufficient to pass downwardlyover the guide piles in the lower short legs of said other substructuresection, said upper and lower short legs being arranged in coaxiallydisplaced References Cited in the file of this patent UNITED STATESPATENTS Quet June 7, 1921 Boschen Nov. 6, 1951 FOREIGN PATENTS GermanyDec. 7, 1950

1. AN OFFSHORE PLATFORM STRUCTURE COMPRISING A FRAMEWORK-TYPE SUBSTRUCTURE MADE UP OF A PLURALITY OF PREFABRICATED TUBULAR-LEGGED SUBSTRUCTURE SECTIONS ADAPTED TO BE POSITIONED ON THE FLOOR OF A BODY OF WATER ONE AT A TIME, EACH OF SAID SUBSTRUCTURE SECTIONS HAVING A PLURALITY OF LONG VERTICAL LEGS OF A LENGTH GREATER THAN THE WATER DEPTH WHEN NORMALLY EXTENDING TO THE WATER BOTTOM AND A PLURALITY OF SHORT VERTICAL LEGS, CROSS-BRACING MEMBERS SECURING THE LONG AND SHORT LEGS TOGETHER TO FORM A FRAMEWORK, AT LEAST ONE OF SAID SUBSTRUCTURE SECTIONS HAVING AT LEAST TWO SHORT LEGS ARRANGED IN THE LOWER PORTION OF THE SECTION ON ONE SIDE THEREOF, A GUIDE PILE EXTENDING THROUGH 